Quartz increases the workability of concrete, can I use it as pozzolan, does it react with cao?
Both former answers are right, however they both fail to make the point. The role of quartz powder in UHPC is reducing the initial porosity of the mixture and thereby increasing the final strength. A pozzolanic reaction of the quartz powder is not only difficult (a little bit might happen on surfaces or cracks), it is even dangerous! If you have (small) aggregates that react, they might behave similarly to aggregates in alkali-silica reaction and induce macroscopic expansion and cracks. This has been observed e.g. for silica fume agglomerates.
So the right answer to your question "can I use it as pozzolan, does it react with cao?" is "no, you can't. Fortunately it reacts very little and therefore you should use it".
All this is valid for curing at normal temperatures, high-temperature curing might change the situation a bit.
Generally, the reactivity of quartz is very low and slow. increasing in the workability may be due to its low reactivity. To enhance its reactivity, high heat or high pH is needed. However, high pH interrupts reaction of Ca by precipitation of Ca ion. If you want quartz pozzlanic reaction, you should use high curing temperature. Please check the reference, "Investigation of hydration and pozzolanic reaction in reactive powder concrete (RPC) using 29Si NMR" by H. Zanni et. al. Quartz may play a role as a filler.
Both former answers are right, however they both fail to make the point. The role of quartz powder in UHPC is reducing the initial porosity of the mixture and thereby increasing the final strength. A pozzolanic reaction of the quartz powder is not only difficult (a little bit might happen on surfaces or cracks), it is even dangerous! If you have (small) aggregates that react, they might behave similarly to aggregates in alkali-silica reaction and induce macroscopic expansion and cracks. This has been observed e.g. for silica fume agglomerates.
So the right answer to your question "can I use it as pozzolan, does it react with cao?" is "no, you can't. Fortunately it reacts very little and therefore you should use it".
All this is valid for curing at normal temperatures, high-temperature curing might change the situation a bit.
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